Helicopters are known which substantially comprise a fuselage; a main rotor on top of the fuselage and rotating about a respective axis; a tail rotor at the end of the fuselage; two horizontal tail surfaces; and two vertical tail surfaces.
More specifically, the rotor substantially comprises a hub rotating about said axis and having a number of blades fixed to and projecting radially from the hub; and a drive shaft connectable to a drive and connected functionally to, to rotate, the hub.
Rotation of the rotor produces high- and low-frequency vibration. More specifically, low-frequency vibration is produced by the wash from the blades and from the centre of the hub striking the vertical and horizontal tail airfoils and the tail rotor itself.
To reduce low-frequency vibration, the rotor comprises a flow deflector fitted to the top centre of the rotor and extending annularly about the rotor rotation axis.
More specifically, the flow deflector is designed to direct flow produced by the rotor in such a manner as to reduce the wash effect and prevent the wash from striking the tail rotor and relative supporting structures.
High-speed rotation of the blades also produces high-frequency vibration, which is transmitted to the drive shaft and therefore to the helicopter.
A need is felt within the industry to reduce generation and transmission of high-frequency vibration to the drive shaft of the rotor, by means of dampers fitted to the rotor and tuned to one or more of the above vibration frequencies. More specifically, a need is felt for compact dampers involving no alteration to the other component parts of the rotor.
A need is also felt within the industry for dampers which, in the event of detachment from the rotor, do not strike, thus producing irreparable damage to, the hub or blades.
Finally, a need is felt within the industry for dampers that do not interfere with the streamline profile of the helicopter or flow deflector, and therefore do not affect airflow induced by the main rotor on the tail rotor and tail airfoils.